U.S. patent application number 11/002646 was filed with the patent office on 2005-07-14 for formation of solid layers on substrates.
This patent application is currently assigned to CONDUCTIVE INKJET TECHNOLOGY LIMITED. Invention is credited to Bentley, Philip Gareth, Fox, James Edward, Hudd, Alan Lionel, Robinson, Martyn John.
Application Number | 20050153078 11/002646 |
Document ID | / |
Family ID | 34743755 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050153078 |
Kind Code |
A1 |
Bentley, Philip Gareth ; et
al. |
July 14, 2005 |
Formation of solid layers on substrates
Abstract
Disclosed is a method of forming on the surface of a substrate a
first solid layer which is suitable for activating a chemical
reaction to form a second layer thereon, the method comprising the
steps of: applying to the surface of the substrate a first liquid
comprising a curable composition and an activator for the second
layer-forming chemical reaction; and curing the curable
composition, thereby forming a first solid layer adhered to the
surface of the substrate, capable of activating the second
layer-forming chemical reaction. A second layer can then be formed
on the substrate by bringing into contact with the first solid
layer a second fluid comprising components of a second
layer-forming chemical reaction, activated by the activator,
thereby causing a second layer to be formed on the first solid
layer.
Inventors: |
Bentley, Philip Gareth;
(Cambridge, GB) ; Fox, James Edward; (Cambridge,
GB) ; Hudd, Alan Lionel; (Nuthampstead, GB) ;
Robinson, Martyn John; (Cambridge, GB) |
Correspondence
Address: |
MORGAN LEWIS & BOCKIUS LLP
1111 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20004
US
|
Assignee: |
CONDUCTIVE INKJET TECHNOLOGY
LIMITED
|
Family ID: |
34743755 |
Appl. No.: |
11/002646 |
Filed: |
December 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60540223 |
Jan 28, 2004 |
|
|
|
Current U.S.
Class: |
427/443.1 ;
252/500; 427/299; 427/372.2; 427/402; 427/437 |
Current CPC
Class: |
C23C 18/1651 20130101;
H01M 4/04 20130101; Y02E 60/50 20130101; Y10T 428/31699 20150401;
C23C 18/2066 20130101; H01M 6/40 20130101; C23C 18/206 20130101;
H01M 4/049 20130101; H05K 2203/0709 20130101; H05K 2203/013
20130101; C23C 18/1608 20130101; C23C 18/1653 20130101; C23C 18/161
20130101; C23C 18/405 20130101; H01M 4/0404 20130101; H05K
2203/1157 20130101; H01M 8/0228 20130101; C23C 18/30 20130101; H01M
4/0416 20130101; H05K 3/182 20130101; H01M 4/0414 20130101; H01M
4/0492 20130101 |
Class at
Publication: |
427/443.1 ;
427/402; 427/372.2; 427/299; 427/437; 252/500 |
International
Class: |
B05D 007/00; B05D
001/36; H01C 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2003 |
GB |
0328221.7 |
Jan 28, 2004 |
GB |
0401825.5 |
Claims
1. A method of forming, on the surface of a substrate, a first
solid layer which is capable of activating a chemical reaction to
form a second layer thereon, the method comprising bringing into
contact the substrate surface and a first liquid comprising a
curable composition and an activator for said second layer-forming
chemical reaction; and curing the curable composition to increase
adhesion of the material to the surface of the substrate, thereby
forming a first solid layer, capable of activating said second
layer-forming chemical reaction after contact with a second
fluid.
2. A method according to claim 1, further comprising bringing into
contact the first solid layer and the second fluid that comprises
one or more reagents for chemical reaction, activated by the
activator, to form the second layer.
3. A method according to claim 2, wherein the second layer
comprises a conductive metal layer.
4. A method according to claim 3, wherein the second layer-forming
chemical reaction is a reaction between metal ions and a reducing
agent, to form a conductive metal region, and the activator
comprises one or more of catalyst metal ions, reducing agent or a
pH-altering reagent.
5. A method according to claim 1, wherein the curable composition
comprises one or more monomers and/or oligomers which can
polymerise and/or cross-link in use, thereby hardening and forming
a solid layer.
6. A method according to claim 5, wherein the curable composition
comprises one or more acrylates or methacrylates.
7. A method according to claim 5 or 6, wherein the curable
composition includes a proportion of monomers and/or oligomers
having at least 3 cross-linkable functional groups.
8. A method according to claim 1, wherein the first liquid is such
that the first solid layer includes a first chemical functionality
that is at least partially insoluble in the second fluid.
9. A method according to claim 1, wherein the first liquid is such
that the first solid layer is permeable to the second fluid.
10. A method according to claim 9, wherein the first solid layer
includes a second chemical functionality which is at least
partially soluble, miscible or swellable in the second fluid, or
otherwise penetrable by the second fluid.
11. A method according to claims 8 and 10, wherein the weight ratio
of the first chemical functionality to the second chemical
functionality is greater than about 5:1, preferably greater than
about 10:1, more preferably greater than about 15:1.
12. A method according to claim 1, wherein the weight ratio of the
curable composition to activator in the first liquid is greater
than about 15:1, preferably greater than about 25:1.
13. A method according to claim 1, wherein the first liquid is
brought into contact with the substrate surface by a printing
process, preferably a non-contact digital printing process.
14. A method according to claim 1, wherein the first solid layer is
formed on the substrate surface according to a pattern.
15. A method according to claim 14, wherein the first liquid is
deposited onto the substrate surface according to a pattern by
digital inkjet printing.
16. A method according to claim 14, wherein the curable liquid is
applied extensively to the substrate surface and selectively cured
according to a pattern.
17. A method according to claim 1, wherein the second fluid is
deposited on the first solid layer by inkjet printing.
18. A method according to claim 1, wherein the curable composition
is curable in response to a stimulus.
19. A method according to claim 18, wherein the curable composition
is curable in response to ultraviolet radiation.
20. A method according to claim 1, wherein the activator comprises
a metal or metal-containing material
21. A method according to claim 20, wherein the weight ratio of the
curable composition to the metal portion of the activator is
greater than about 15:1, preferably greater than about 25:1.
22. A method according to claim 20 or 21, wherein the activator
comprises a catalyst.
23. A method of fabricating an electrical item comprising the
method of any one of claim 1.
24. A method according to claim 1, for use in producing a
battery.
25. A method according to claim 1, for use in producing an
electrical connection between two components of a circuit.
26. A method according to claim 1, for use in producing a
decorative feature.
27. An article prepared according to the method of claim 1.
28. A liquid comprising a curable layer-forming composition for
forming a first solid layer on the surface of a substrate, the
liquid comprising an activator suitable for activating a second
layer-forming chemical reaction, and a curable composition capable
of being cured to increase adhesion of the material to the surface
of the substrate and to form a first solid layer adhered to a
substrate and capable of activating said second layer-forming
chemical reaction.
Description
FIELD OF THE INVENTION
[0001] The invention relates to formation of layers on substrates,
particularly, but not exclusively, the formation of conductive
metal regions on substrates by the reduction of metal ions.
BACKGROUND TO THE INVENTION
[0002] There are numerous industrial applications in which it is
desirable to form a solid layer of a material on the surface of a
substrate. For example, it is desirable to form a conductive metal
layer in applications as diverse as the manufacture of printed
circuit boards, aerials, and antennae such as those found in mobile
telephones, radio frequency identification devices (RFIDs), smart
cards, contacts for batteries and power supplies, arrays of
contacts for flat screen technologies (liquid crystal displays,
light emitting polymer displays and the like), electrodes for
biological and electrochemical sensors, smart textiles and
decorative features.
[0003] In this specification, unless the context requires
otherwise, the adjective solid, in the context of a solid layer, or
solid substrate, refers to being in the solid (rather than liquid
or gas) phase of matter. A solid layer or substrate may be plastic,
elastic, resilient, rigid, gelatinous, permeable or have any other
property consistent with being solid phase.
[0004] In some of these applications, the solid layer that is
formed covers the surface. In other applications, the solid layer
is patterned, and the accuracy and fineness of detail of the
pattern can be important. For example, printed circuit boards may
have intricate patterns of copper conductive tracks. Accuracy and
fineness of detail is important in determining the extent of
miniaturisation possible on such printed circuit boards, and the
reliability of the electronic circuits built thereon.
[0005] Some methods of forming a solid layer on a surface of a
substrate require a catalyst, or other activator. For example, the
electroless plating process is a solution chemistry plating
technique which has been used for many years to apply a conductive
metal coating layer to a substrate surface, which can be flat or
shaped. In the electroless process, a substrate is immersed in a
succession of baths in turn.
[0006] An example of the electroless process used to form a copper
layer on the surface of a substrate would be as follows:
[0007] Firstly, a plastics substrate is etched in a chromic
acid/concentrated sulphuric acid bath at 68.+-.2.degree. C. to
microscopically etch the surface of the plastics substrate,
ensuring good adhesion of the copper to the surface of the plastics
substrate.
[0008] Secondly, any hexavalent chromic species left on the
plastics substance are neutralised in a bath comprising
approximately 30% concentrated hydrochloric acid at around
50.degree. C. The plastics substrate is then added to a third bath
in which an activator is added to prepare the plastics substrate
surface to absorb the catalyst in the next step. This third bath is
typically approximately 30% concentrated hydrochloric acid, at room
temperature.
[0009] Next, the plastics substrate is dipped into a fourth bath,
which includes a dilute solution of a palladium colloid along with
tin salts. A colloid deposits on the surface of the plastics
material to catalyse the deposition of copper in the subsequent
plating steps. This bath includes a high proportion of tin salts,
approximately 30% concentrated hydrochloric acid, and is operated
at room temperature.
[0010] The fifth bath into which the plastics substrate is dipped
includes an accelerator which activates the absorbed palladium,
improving the speed and uniformity of deposition. Accelerator baths
include around 30% concentrated hydrochloric acid.
[0011] Finally, the activated plastics substrate is dipped into a
sixth bath including a plating solution which, catalysed by the
palladium colloid on the plastics substrate, causes copper to
deposit onto areas of the plastics substrate which were coated with
the catalyst. The plating solution includes a copper salt,
formaldehyde as a reducing agent, and sodium hydroxide to activate
the formaldehyde. The composition of the plating solution must be
carefully temperature controlled, with a temperature of
45.+-.2.degree. C. being appropriate for some commercially
applicable compositions.
[0012] In the above example chemistry, the catalyst is required for
formation of the copper layer, and the acid pre-treatment step is
important as it helps the resulting metal layer adhere to the
substrate.
[0013] Various alternatives to this chemistry are known.
[0014] For example, WO 2004/068389 describes a method of forming a
conductive metal region on a substrate, comprising depositing on
the substrate a solution of a metal ion, and depositing on the
substrate a solution of a reducing agent, such that the metal ion
and the reducing agent react together in a reaction solution to
form a conductive metal region on the substrate. In some
embodiments, a catalyst or other activator is required to start the
reaction which forms the conductive metal region. In general, a
catalyst is applied to a substrate surface, which is then brought
into contact with the chemical composition which reacts, catalysed
by the catalyst, to deposit a metal on the surface of the
substrate.
[0015] It is known to deposit on a substrate, e.g by inkjet
printing, a catalyst for a metal-forming reaction, with the
catalyst applied in a solution containing a polymeric binder. See,
for example, WO 02/099162 which discloses use of binders such as
ethyl cellulose.
[0016] U.S. Pat. No. 6,495,456 discloses formation of electrodes on
a chip substrate by a process that involves applying a photo-active
catalyst liquid (of unspecified composition) to a chip substrate,
irradiating the substrate with light to activate irradiated
portions of the liquid (possibly selectively, e.g. using a mask)
and then using electroless plating to form metal on the activated
portions.
[0017] It is known to use ultra violet radiation and other means to
reduce palladium acetate deposited on a substrate to palladium
metal, followed by electroless plating of copper. Reduction may be
performed selectively, by use of a contact mask, to produce
patterned catalyst. Alternatively, palladium produced by infra red
treatment may be patterned by excimer laser ablation using a metal
contact mask. See Zhang et al "VUV light-induced decomposition of
palladium acetate films for electroless copper plating" Applied
Surface Science 109/110 (1997) 487-492 and Esrom "Past selective
metal deposition on polymers by using IR and excimer VUV photons"
Applied Surface Science 168 (2000) 1-4.
[0018] U.S. Pat. No. 3,900,320 discloses a process for metallizing
a plastic or ceramic base. A pre-plate solution comprising a
compound of catalytic metal, such as a palladium salt, binder
material such as one or more polymers and solvent are coated on the
base and dried so as to form a thin polymer layer of about 20
Angstrom to about 3000 Angstrom thick which may thereafter be
directly plated by contact with an electroless plating solution.
The pre-plate solution has specified viscosity characteristics and
specified high concentration levels of catalytic metal compound. A
photosensitive polymer former can be used as a component of the
pre-plate solution specifically for photographically developing a
plateable pattern on a substrate such as a circuit board, printing
plate or the like.
SUMMARY OF THE INVENTION
[0019] In accordance with the invention there is provided a method
of forming, on the surface of a substrate, a first solid layer
which is capable of activating a chemical reaction to form a second
layer thereon, the method comprising bringing into contact the
substrate surface and a first liquid comprising a curable
composition and an activator for said second layer-forming chemical
reaction; and curing the curable composition to increase adhesion
of the material to the surface of the substrate, thereby forming a
first solid layer adhered to the surface of the substrate, capable
of activating said second layer-forming chemical reaction after
contact with a second fluid.
[0020] A curable composition is one which can undergo a chemical
change resulting in hardening, preferably solidification. The
hardening process improves adhesion of the material and results in
formation of a solid layer (the first solid layer), that may be
rigid, plastic, elastic, resilient, gelatinous, permeable or have
any other property consistent with being in the solid phase, as
opposed to liquid or gas. The solid layer may include regions in
liquid or gaseous form.
[0021] The curable composition is such that the resulting first
solid layer adheres to the substrate, and so is selected having
regard to the substrate. Adhesion can arise through chemical
bonding, physical bonding, mechanical bonding or a mixture thereof.
Use of a curable composition can result in improved adhesion to a
wider variety of different substrates than is possible with
non-curable catalytic solutions of the prior art.
[0022] The curable composition is brought into contact with the
substrate surface while the composition is in liquid form, and is
subsequently cured. Curing typically takes place while the curable
composition is still in liquid form, although the curable
composition may instead be converted to solid form, e.g. by drying,
prior to curing.
[0023] The activator is typically incorporated in the first solid
layer, whether by entrapment, immobilisation or other means, and is
typically dispersed throughout the first solid layer within a
matrix formed by the cured composition. The activator is thus
adhered with respect to the substrate by virtue of its inclusion in
the first layer.
[0024] The curable composition typically comprises one or more
component chemicals which can undergo a reaction resulting in
hardening, preferably solidification.
[0025] Preferably, the curable composition comprises one or more
monomers and/or oligomers which can polymerise and/or cross-link in
use, thereby hardening and forming a solid layer. Preferably, the
resulting product forms a matrix, typically a polymer matrix, which
includes the activator. A curable composition including at least
some oligomers will often have lower toxicity than if only monomers
were included. The presence of at least some oligomers can also
result in production of a first layer having improved physical
properties such as flexibility, hardness and
abrasion-resistance.
[0026] The curable composition is curable in response to
appropriate curing conditions. For example, the composition may be
curable in response to a stimulus, such as electromagnetic
radiation of a particular wavelength band (e.g. ultra-violet, blue,
microwaves, infra-red), electron beams, or heat. The composition
could instead be curable in response to appropriate chemical
conditions, particularly the presence of a chemical curing agent or
hardener: in this case a "two pack" approach may be adopted, with
one chemical component applied in the first liquid and a second
chemical component separately applied (simultaneously or
subsequently). As a further possibility the composition may be
curable in response to the presence of species such as moisture or
air. Preferably, the curable composition is selected to undergo a
reaction responsive to one or more of the above stimuli. An
ultra-violet curable composition is currently preferred.
[0027] It is preferred to use a first liquid such that no
significant or substantial heating is required. This means that the
method of the invention can be used with a wide range of
substrates, including heat-sensitive plastics materials. In
particular, it is preferred that the first layer is formed at
temperatures below about 300.degree. C. (allowing the use of
polyimide substrates), desirably below about 200.degree. C.
(allowing the use of polyester substrates such as Teonex (Teonex is
a Trade Mark)), more desirably below about 100.degree. C. (allowing
use of a wide range of themoplastic substrates), yet more desirably
below about 50.degree. C. (allowing use of low Tg substrates) and
possibly at room temperature, avoiding the need for heating.
Heating, if required, is only applied for a relatively short time,
typically less than 15 minutes and preferably less than about 2
minutes for processing efficiency.
[0028] Typically, the curable composition comprises one or more
monomers and/or oligomers which can form a polymer, and an
initiator which starts a polymerisation reaction responsive to a
stimulus, as discussed above. Suitable initiators are well known to
those skilled in the art. For example, benzoyl peroxide, lauryol
peroxide, azobis-(1-hydroxycyclohexane- ) or AIBN
(2,2'-azobisisobultyronitile) (all from Polysciences, Inc., USA)
can be included to initiate a polymerisation reaction responsive to
heat. Darocur 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one),
Irgacure 184 (1-hydroxy-cyclohexylphenyl-ketone), Irgacure 369
(2-benzyl-2-dimethylami- no-1-(4-morpholinophenyl)-butanone-1),
Irgacure 651 (2,2-dimethoxy-1, 2-diphenylethan-1-one), Irgacure
2959 (1-[4-(2-hydroxyethoxy)-phenyl]-2-h-
ydroxy-2-methyl-1-propane-1-one), Irgacure 819 and Irgacure 1700
(Darocur and Irgacure are Trade Marks) are examples of UV
photo-intiators, available from Ciba Speciality Chemicals,
Manchester, UK and Basel, Switzerland. Typically, such initiators
generate free radicals responsive to a stimulus. Other curing
processes can be used, such as cationic curing of materials such as
epoxys, vinyl ethers and vinyl esters, where an initiator generates
cations responsive to a stimulus.
[0029] Conveniently, the monomers and/or oligomers are those known
from the field of UV curable inks, or other curable inks, proposed
for inkjet printing of curable inks. Suitable UV-curable materials
include acrylates and methacrylates, particularly those included in
the following list classified by the number of cross-linkable
functional groups:
[0030] Monofunctional
[0031] Isobornylacrylate (IBOA), e.g. as SR506D
[0032] Octyl decyl acrylate (ODA), e.g. as SR484
[0033] Caprolactone acrylate, e.g. as SR495
[0034] Lauryl acrylate, e.g. as SR335
[0035] Difunctional
[0036] Tripropylene glycol diacrylate (TPGDA), e.g. as Actilane
424
[0037] 1,6-hexanediol diacrylate (HDDA), e.g. as Actilane 425
[0038] Dipropylene glycol diacrylate (DPGDA), e.g. as SR508
[0039] Propoxylated(2) neopentyl glycol diacrylate (PONPGDA), e.g.
as SR9003
[0040] Tricyclodecanedimethanol diacrylate (TCDDMDA), e.g. as
SR833S
[0041] Polyethylene glycol 400 diacrylate (PEG400DA), e.g. as
SR344
[0042] Trifunctional
[0043] Trimethylol propane triacrylate (TMPTA), e.g. as Actilane
431
[0044] Ethoxylated(3) trimethylol propane triacrylate, e.g. as
SR454
[0045] Ethoxylated(6) trimethylol propane triacrylate, e.g. as
SR499
[0046] Tetrafunctional
[0047] Actilane 505 (a tetrafunctional polyester acrylate
oligomer)
[0048] Ethoxylated pentaerythritol tetraacrylate (PPTTA), e.g. as
Actilane 440
[0049] Ditrimethylolpropane tetraacrylate (di TMPTA), e.g. as
Actilane 441
[0050] Hexafunctional
[0051] Dipentaerythritol hexaacrylate (DPHA), e.g. as Actilane
450
[0052] The Actilane range is available from Akzo Nobel, The
Netherlands. Actilane is a Trade Mark.
[0053] The SR range is available from Sartomer, USA.
[0054] All of the above acrylates cure in response to free
radicals, e.g. generated from an initiator such as Irgacure 819 and
Irgacure 1700. All of the above acrylates are in the form of
liquids, although it is instead possible to use solid monomers
and/or oligomers.
[0055] It is preferred that some (but not all) of the monomers
and/or oligomers have at least 3 cross-linkable functional groups,
e.g. being selected from the trifunctional, tetrafunctional and
hexafunctional materials listed above. Use of such materials
results in production of polymers that are more highly cross-linked
than polymers formed from monomers and/or oligomers with fewer
cross-linkable functional groups, and can provide a stronger, more
robust film with better adhesion to the substrate. Too high a
proportion of such highly cross-linkable monomers and/or oligomers
(having at least 3 cross-linkable functional groups) would,
however, tend to form a brittle surface and so should be avoided.
In addition, use of too high a proportion of such highly
cross-linkable materials would tend to produce a curable
composition of too high viscosity to be suited to inkjet
printing.
[0056] In general, the higher the number of cross-linkable
functional groups, the higher the viscosity of the monomer/oligomer
and so the smaller proportion of the monomer/oligomer it is
appropriate to use. As an approximate guide, trifunctional
materials should not exceed about 75% by weight of the total
monomer/oligomer content of the first liquid, tetrafunctional
materials should not exceed about 35% by weight of the total
monomer/oligomer content or the first liquid, and hexafunctional
materials should not exceed about 10% by weight of the total
monomer/oligomer content of the first liquid.
[0057] The method conveniently includes formation of the second
layer on the first solid layer. The method thus preferably further
comprises bringing into contact the first solid layer and a second
fluid that comprises one or more reagents for chemical reaction,
activated by the activator, to form the second layer. The second
fluid contacts the activator in the first layer, and reacts to form
the second layer on the first solid layer.
[0058] The first solid layer need not necessarily finish caring
before the second fluid is applied.
[0059] The second layer of material is typically solid and is
conveniently a conductive metal layer, which may be formed by a
variety of different processes involving the activator in the first
layer. The processes typically involve the reduction of metal ions,
and include electroless plating, as referred to above, and the
process disclosed in WO 2004/068389.
[0060] The improved adhesion of the first layer to the substrate
surface made possible by the invention, as noted above, results in
improved adhesion of such a conductive metal layer, and makes it
possible to produce a thicker layer of metal, e.g. copper, without
blistering or peeling of the layer from the substrate.
[0061] As the activator is located in a layer on the surface of the
substrate, the second reaction, e.g. metallisation, will generally
occur on or in the first layer in preference to reaction, e.g. the
formation of fine particles of metal, in the second fluid.
[0062] The second fluid may be in the form of one or more
components, that may be applied to the first solid layer
simultaneously or sequentially.
[0063] The first layer need not be directly adhered to the
substrate surface: there may be one or more intervening layers.
Further, the second layer need not be the top or final layer: one
or more further layers may be formed thereon.
[0064] The method of the invention allows greater choice of
substrate for a given second layer, and vice versa, than would
otherwise be possible. By selecting an appropriate first liquid,
such that the first solid layer adheres well to the substrate and
the second layer adheres well to the first solid layer, the second
layer may in some cases be more securely affixed with respect to
the substrate than if the second solid layer were adhered directly
to the substrate. This can allow a greater choice of substrate for
a given second layer and/or allows a thicker second layer to be
formed than would be the case if the activator were applied by a
different technique.
[0065] The activator is preferably a catalyst, such as palladium
for catalysing a metallisation reaction. However, the activator
could instead comprise a chemical species which can activate the
second layer forming chemical reaction, but is consumed or reacts
in the process, and so is not strictly speaking a catalyst.
[0066] The activator may alternatively comprise a reagent, or a
plurality of reagents which, when brought into contact with a
second fluid comprising components (preferably other components) of
a second solid-layer-forming chemical reaction, undergo a chemical
reaction leading to formation of a second layer on the first solid
layer.
[0067] The activator may be applied in precursor form. In this
case, the method may include the erter step of chemically
converting the one or more precursor reagents to an active or
catalytic form. For example, palladium acetate may be reduced in
situ by a subsequently applied reducing agent solution, forming
palladium metal which can catalyse deposition of metal thereon when
an appropriate second fluid is applied.
[0068] The first solid layer may coat most or all of the entire
substrate surface. Alternatively, the first solid layer may be
formed on the substrate according to a pattern. This may be
achieved in several ways. For example, the first liquid may be
deposited according to a pattern, e.g. by printing in the desired
pattern, particularly by inkjet printing. Alternatively, the first
solid layer may be patterned after the first liquid has been
deposited; for example, the first liquid may be applied extensively
across the substrate, selectively cured according to a pattern and
uncured liquid may then be removed. Selective curing according to a
pattern can be achieved by use of a mask, such as a shadow mask for
liquid or solid layers or a contact mask for solid layers, to limit
exposure to a stimulus as discussed above, e.g. UV radiation. Laser
writing (using a laser of appropriate wavelength for a particular
initiator) and electron beam writing can also be used. With
electron beam writing, a photoinitiator is not required, and this
approach can be used to create patterns with very fine features, of
the order of 10 nm. As a further possibility, when using chemical
curing, a curing agent or hardener may be selectively applied
according to a desired pattern. In all cases, excess (uncured)
material may be removed by techniques including washing, spraying
or immersion in suitable reagents such as an acid, alkali or
solvent or by physical means such as use of an air knife.
[0069] Thus, the use of a curable composition can allow patterning
to an extent which would not be possible were the activator
deposited on the substrate as a liquid which remained soft and
flowed.
[0070] The first liquid can be applied extensively to a substrate
surface by a wide range of possible techniques, including using
printing, dipping, spraying and spinning techniques such as jet
printing, inkjet printing, spin coating, dip coating, spray
coating, aerosol spraying, roller coating, curtain coating, screen
printing, litho printing, flexo printing, gravure printing and pad
printing, or by any other liquid application technique.
[0071] Preferably, the first liquid is brought into contact with
the substrate by a deposition process, for example a printing
process. Preferably, the deposition process is a non-contact
process that is preferably digital e.g. inkjet printing. The first
liquid is preferably applied as a single liquid, e.g. by inkjet
printing from a single liquid reservoir.
[0072] Printing processes typically result in production of a first
solid layer having a thickness greater than 300 nm and possibly
significantly thicker.
[0073] The first liquid is typically in the form of a solution,
preferably a partially or entirely non-aqueous solution, but may
alternatively be in the form of a suspension or dispersion with one
or more components in solid or colloidal form, or an emulsion.
Different ingredients of the first liquid may be present in
different forms. The first liquid generally includes a carrier
liquid (which may function as a solvent e.g. for the activator),
which is preferably partially or entirely non-aqueous. Preferred
non-aqueous liquids are discussed below. The carrier liquid may be
constituted by one or more curable monomers and/or oligomers, e.g.
as discussed above, if in liquid form, or may be constituted by a
separate liquid (not part of the curable composition) performing a
carrier function only.
[0074] The second fluid is preferably in liquid form, and so is a
second liquid.
[0075] The second liquid may be in the form of a solution,
preferably an aqueous solution, but may alternatively be in the
form of a suspension or dispersion with one or more components in
solid or colloidal form, or an emulsion. The second liquid thus
generally includes a carrier liquid (which may function as a
solvent). The carrier liquid of the second liquid preferably
comprises water.
[0076] The first liquid desirably includes a carrier liquid that is
sufficiently aggressive to the substrate to allow the first liquid
to penetrate therein, with the carrier liquid partially dissolving
or otherwise permeating into the substrate, increasing adhesion of
the first solid layer to the substrate, and thus also increasing
the adhesion of the second layer to the substrate (via the first
solid layer).
[0077] The first liquid and the second liquid preferably comprise
different carrier liquids. This allows the carrier liquid of the
first liquid to be selected to be appropriate for the formation of
the first layer and the adhesion of the first layer to the
substrate, whilst the carrier liquid of the second liquid can be
selected to be appropriate for the formation of the second layer.
Preferably, the carrier liquid of the second liquid is water. Thus,
aqueous metallisation chemistry and a non-aqueous first stage can
be utilised in different steps of the same process. Preferably, the
carrier liquid of the first liquid is partially or entirely
non-aqueous.
[0078] Typically, print quality and adhesion are governed
predominantly by the properties of the first liquid and the first
solid layer which it forms. Thus, to some extent, the invention
allows the first liquid to be selected dependent on the patterning
quality required and the second fluid to be selected dependent on
the desired properties of the second layer. This can allow greater
flexibility in designing appropriate first liquid and second fluid
chemistries for a particular application.
[0079] The first liquid may be selected to have improved wetting
properties on one or more substrates as compared with those of the
second fluid. This allows more accurate and precise patterning than
if the first liquid was applied from the same carrier liquid (e.g.
water) as the second fluid, with fine features and better edge
definition being possible. There will typically be less bleed and
feathering of the first liquid than if activator were applied to
the surface by a different technique using a carrier with poorer
wetting properties. Improved wetting properties allow more accurate
and precise patterning as successive spots of liquid along a line
can be deposited further apart (by a technique such as inkjet
printing) allowing a lower volume of liquid to be used, and thus
narrower lines and finer features to be prepared.
[0080] This use of the first liquid comprising an activator is
particularly beneficial when using inkjet printing to deposit a
material on a substrate. Many curable liquids have an appropriate
viscosity to be suitable to be inkjet printed, giving good print
head performance. Suitable viscosities for inkjet printing liquids
are typically in the range 1 to 20 cPs at print head operating
temperature.
[0081] The process may be repeated (optionally with different first
liquids and second fluids) to build up a multi-layer structure.
[0082] The first solid layer preferably includes a first chemical
functionality which is at least partially insoluble in the second
fluid, as disclosed in our International Application
PCT/GB2004/004589. This means that the physical integrity of the
first layer is maintained on contact with the second fluid and
while the second layer is formed. This has the consequence of
improving adhesion of the second layer with respect to the
substrate surface. The first chemical functionality need not be
completely insoluble in the second fluid, but merely sufficiently
insoluble to achieve this effect. Thus, the first chemical
functionality only needs to be sufficiently insoluble in the second
fluid to retain the integrity of the first layer while the second
layer is formed.
[0083] The second fluid is preferably aqueous, as noted above, so
the first chemical functionality is preferably at least partially
insoluble in water. The first chemical functionality may be present
in the first liquid, and also in the first layer, or may be formed,
e.g. by cross-linking, in the first layer from reactants (that are
possibly soluble in the second fluid) in the first liquid. The
first chemical functionality is preferably non-ceramic. The first
chemical functionality is preferably at least predominantly or
fully organic and/or silicon based, comprising at least 50% by
weight of organic and/or silicon materials, for improved adhesion
to a wide range of organic substrates such as plastics substrates.
The first chemical functionality may absorb the second fluid and
swell. The first chemical functionality may be constituted by the
reaction product of the curable composition, e.g. one or more
curable monomers and/or oligomers in the first liquid. Such
materials may be included in the first liquid and react to form a
polymer in the first layer with appropriate solubility properties.
The polymer product also has good adhesion to a very wide range of
substrates, including metals, glass, ceramics and plastics
materials. Thus, the first liquid preferably includes one or more
ingredients that constitute or form the first chemical
functionality in the first layer.
[0084] Preferably, the components of the first liquid are selected
so that the first solid layer is permeable to the second fluid when
the second fluid is brought into contact with the first solid
layer, as disclosed in our International Application
PCT/GB2004/004589. We have found that this can substantially
improve the effective activation/catalytic activity of the first
solid layer. In particular, the second fluid can penetrate the
first solid layer, allowing the second fluid to access the
activator within the first solid layer. The second layer-forming,
reaction can thus take place on, or in close proximity to, the
substrate surface, producing the desired second layer of material
on the substrate. Furthermore, penetration of the second fluid into
the first solid layer may result in the second layer of material
intermingling with the first solid layer, thereby enhancing
adhesion of the second layer of material to the substrate via the
adhered first solid layer and improving through layer conductivity
(where the second layer is conductive from its top surface down to
the surface of the substrate).
[0085] The first layer thus preferably comprises a second chemical
functionality which is at least partially soluble, miscible or
swellable in the second fluid or permeable to the second fluid, as
disclosed in our International Application No. PCT/GB2004/004589.
The second fluid is preferably aqueous, as noted above, so the
second chemical functionality is preferably at least partially
soluble or swellable in water or permeable to water. The second
chemical functionality may be present in the first liquid, and also
the first layer, or may be formed in the first layer from reactants
in the first liquid. Suitable second chemical functionalities are
discussed below, and include polyvinylpyrrolidone (PVP), which is
soluble in water, and which may be included as an ingredient of the
first liquid. The second chemical functionality will at least
partially dissolve or swell in, or be permeable to, the second
fluid, allowing the fluid to penetrate the first solid layer and
contact the activator. The first chemical functionality retains
sufficient integrity to adhere to the substrate and the second
layer, resulting in a "sponge-like" structure. This has the
consequence of permitting enhanced access to the activator than
would otherwise be the case, allowing the use of lower
concentrations of activator, with consequential cost savings. In
particular it is possible to use a first liquid with a weight ratio
of curable composition to activator of greater than about 15:1,
preferably greater than about 25:1. The ability to be able to use
relatively low proportions of activator in the first liquid has the
benefit of allowing greater freedom in formulation of the first
liquid, e.g. in terms of properties such as viscosity and solvent
choice.
[0086] Thus, the first liquid may comprise one or more ingredients
which constitute or form in the first layer a second chemical
functionality which is at least partially soluble, miscible or
swelleable in the second fluid or permeable to the second fluid.
One preferred second chemical functionality is polyvinylpyrrolidone
(PVP), which is soluble in water. Alternatives include polyacrylic
acid, polyvinyl acetate, polyethylene imine, polyethylene oxide,
polyethylene glycol, gelatin or copolymers thereof. The soluble
components may dissolve when the second fluid is brought into
contact with the first solid layer. For example, the
polyvinylpyrrolidone will dissolve in contact with an aqueous
solution of metal ion and reducing agent usable to form a
conductive metal region on the first solid layer (see below).
Around 5% by weight of polyvinylpyrrolidone in the resulting solid
layer is appropriate.
[0087] The first liquid could instead (or as well) comprise a water
swellable monomer and/or oligomer such as HEMA (2-hydroxyethyl
methacrylate), GMA (glyceryl methacrylate) or NVP (u-vinyl
pyrrollidinone). Other monomers and/or oligomers which are
themselves swellable in the second fluid and/or are swellable when
polymerised could be used instead. This allows the second fluid to
permeate into the first solid layer, improving adhesion and
allowing access to more activator than just activator present on
the surface of the first solid layer.
[0088] The first liquid could instead (or as well) comprise a high
boiling point solvent miscible with the second liquid, with the
high boiling point solvent remaining in liquid form in the first
solid layer. For example, NMP (n-methylpyrrolidinone) could be used
when the second liquid is aqueous. This keeps the first layer
matrix open allowing penetration by the second liquid and improving
the adhesion of the second layer to the first solid layer. Other
suitable solvents include ethylene glycol, diethylene glycol or
glycerol.
[0089] The first liquid could instead (or as well) comprise
micro-porous particles to create a micro-porous film structure.
Micro-porous particles could be organic (e.g. PPVP (poly
(polyvinylpyrrolidone))) or inorganic (e.g. silica).
[0090] The weight ratio of the first chemical functionality to the
second chemical functionality is preferably greater than about 5:1,
more preferably greater than about 10:1, most preferably greater
than about 15:1. The use of relatively large amounts of the first
chemical functionality results in benefits of improved adhesion to
the substrate surface, more rapid curing, durability of the
resulting first solid layer, and improved formulation flexibility
for the first liquid.
[0091] The first liquid may include a carrier liquid which is
volatile and which evaporates off, partially or fully, after
application to the substrate For example, the first liquid may
comprise water or (preferably) one or more organic solvents which,
in use, are evaporated off before the second fluid is brought into
contact with the first layer. The method in this case may include a
pause to allow a volatile carrier to evaporate before one or both
of applying a stimulus (if applicable) and bringing the second
fluid into contact with the first layer. It may be advantageous for
some of the carrier liquid to remain in the first solid layer in
liquid form, to keep the first layer matrix open.
[0092] Preferably, however, no significant delay between depositing
and curing the first liquid is required, and there is no need for
drying or pre-curing steps. This reduces over-wetting of the
substrate, which causes loss of definition to the image. Preferably
the delay between deposition and curing is 20 seconds or less.
Further, the curing process itself can be achieved very rapidly,
typically in less than 1 second, with benefits of control of image
quality.
[0093] Where the carrier liquid is constituted by liquid
monomers/oligomers, substantially all of the constituents of the
first liquid may remain in the first solid layer, albeit possibly
in chemically changed form.
[0094] As the activator is also included in the first liquid, it
will typically be trapped within the first layer in a matrix
formed, for example, by a polymer. The activator could also be
immobilised as part of the matrix, for example, by including the
activator on a molecule with a reactive group which reacts with
monomer or oligomer units. The activator may be initially inactive,
and become active only once the first liquid has been cured, or in
response to a stimulus, or when in contact with a component of the
second fluid.
[0095] The invention finds particular application in the production
of layers of conductive metal as the second solid layer. Conductive
metal layers are typically formed by the reduction of metal ions in
a reaction involving a catalyst, a metal ion and a reducing agent.
A variety of different techniques may be used, including
electroless plating and the process disclosed in WO 2004/068389.
One reagent of the process, typically the catalyst, is deposited on
a substrate (typically by inkjet printing) in the first layer by
the method of the invention, and other necessary reagents deposited
(by inkjet printing, immersion or otherwise) in the second fluid
(and possibly in one or more other vehicles) resulting in reaction
to form a conductive metal layer constituting the second solid
layer.
[0096] In embodiments of the invention where the second layer is a
conductive metal region, formed by the reaction of metal ions and a
reducing agent, the activator conveniently comprises a metal or
metal-containing material, typically a catalyst or catalyst
precursor. Suitable metals include metal colloids or particles,
such as colloids or particles of platinum, silver, palladium,
iridium, bronze, aluminium, gold or copper. Suitable
metal-containing materials include salts or complexes of a
conductive metal, preferably salts of a transition metal,
particularly palladium, platinum and silver. The salts may be
inorganic, such as palladium chloride, or organic, for example
palladium acetate or palladium propanoate. Preferred organic salts
are alkanoates. The current preferred activator is palladium
acetate. Desirably the weight ratio of the curable composition to
the metal portion of the activator is greater than about 15:1,
preferably greater than about 25:1.
[0097] A suitable solvent for the deposition of an organic acid
salt of a transition metal, e.g. palladium acetate, include
diacetone alcohol, a 50/50 mixture of equal parts by weight of
diacetone alcohol and methoxy propanol, and a 50/50 mixture of
equal parts by weight of toluene and methoxy propanol. A co-solvent
is preferably included to increase viscosity to suitable levels for
inkjet printing. The salt, e.g. palladium acetate, is conveniently
present in an amount in the range 1 to 3% by weight, preferably
about 2% by weight of the deposited liquid.
[0098] Where the activator is a catalyst or catalyst precursor, the
second fluid conveniently comprises a solution of a metal ion and a
reducing agent, operable to react together, activated by the
activator, to form a conductive metal region on the first solid
layer. Preferably, the composition of the second fluid is such that
it does not react spontaneously, but reacts only once it has been
brought into contact with the activator present in the first solid
layer. The second fluid may further comprise pH-altering reagent
such as an acid or a base, to activate the reducing agent.
[0099] The metal ion, the reducing agent and the optional base/acid
may be deposited in two or three separate component solutions which
mix together on the substrate to form a reaction solution. Further
details may be as disclosed in WO 2004/068389.
[0100] Where the second layer-forming chemical reaction is to be a
reaction between metal ions and a reducing agent, to form a
conductive metal region, instead of being a catalyst or catalyst
precursor, the activator may be one or more of metal ions, reducing
agent or a pH altering reagent such as an acid or base. The second
fluid will be such that a second-layer-forming reaction begins when
the second fluid is in contact with the first layer. Where the
activator comprises metal ions, typically as metal salts or metal
complexes (and perhaps also acid/base), the second fluid may
comprise reducing agent, possibly with appropriate pH adjusting
reagent, e.g. a base in the case of formaldehyde. The second fluid
may also contain additional ions of the same or a different metal.
The activator could be metal particles or colloids. Where the
activator comprises a reducing agent (and perhaps also base or
acid), the second fluid will preferably comprise metal ions,
typically as metal salts or metal complexes. The second fluid may
comprise further reducing agent which may be the same or different
to the first reducing agent. It may be appropriate to use a more
powerful reducing agent such as DMAB (dimethylamineborane)
initially followed by a less powerful reducing agent such as
formaldehyde which gives a more pure, higher conductivity metal
layer. Where the activator comprises pH altering reagent, the
second fluid typically includes metal ions and reducing agent, and
optionally further pH altering reagent.
[0101] The metal ion may be an ion of any conductive metal,
particularly a transition group metal. Preferred conductive metals
include copper, nickel, silver, gold, cobalt, a platinum group
metal, or an alloy of two or more of these materials. The
conductive metal may include non-metallic elements, for example,
the conductive metal may be nickel phosphorus.
[0102] The metal ion is typically in the form of a salt, for
example copper sulphate. The metal ion might instead be present in
a complex such as with EDTA (ethylene diamine tetra acetic acid) or
cyanide.
[0103] Examples of appropriate reducing agents are formaldehyde,
glucose or most other aldehydes, or sodium hypophosphites, or
glyoxylic acid or DMAB (dimethylamineborane).
[0104] Optionally, the substrate is preheated before the first
liquid is deposited thereon This causes the liquid to dry rapidly
and spread less, achieving thinner lines. For example, a Melinex
polyester substrate (Melinex is a Trade Mark) may be heated with
air at 350.degree. C. for 4 seconds using a hot air gun.
[0105] Preferably, the first liquid is deposited onto the substrate
by inkjet printing. The second fluid may be deposited on the first
layer by inkjet printing or other techniques. Where the first
liquid and/or resulting first layer are patterned, the second fluid
may be deposited according to the same pattern.
[0106] As inkjet printing processes are typically digitally
controlled, different patterns can be applied using the same
apparatus to different substrates. This is particularly important
for the production of one-off products, customised products, or a
series of uniquely identifiable products.
[0107] The substrate may be selected from a wide range of
possibilities, including plastics, ceramics, natural materials,
fabrics etc. In embodiments where the second layer is a conductive
metal, suitable substrates include plastics materials and fabrics,
e.g. in the form of sheets. A substrate might be a material having
thereon electrical components, such as conductive, semi-conductive,
resistive, capacitive, inductive, or optical materials, such as
liquid crystals, light emitting polymers or the like. As noted
above, the method of the invention need not involve significant
heating and so may be used with a wide range of substrates,
including heat-sensitive plastics materials. The method may include
the step of depositing one or more of said electrical components on
the substrate, preferably by inkjet printing, prior to forming a
conductive metal region on the resulting substrate.
[0108] Similarly, the method may further include the step of
depositing an electrical component onto the resulting conductive
metal region, building up complex devices. Said further deposition
step may also be carried out using inkjet printing technology.
[0109] The invention finds particular application in printing of
batteries. A battery may be formed on a substrate by forming two
regions of different conductive metals on a substrate by the method
of the invention, and electrolytically connecting the two regions
by way of an electrolyte (which may be inkjet printed), thereby
forming an electrochemical cell. A plurality of electrochemical
cells may be electrically connected in series or in parallel
thereby increasing the voltage and/or current available. The
invention also covers a method of forming a battery by forming two
regions of different conductive metals on a substrate by the method
of the invention and electrolytically connecting the two regions by
way of an electrolyte (which may be inkjet printed). The invention
also extends to a battery formed by the said method.
[0110] Thus, the method can be used as one stage in the fabrication
of electrical items. It is particularly appropriate for use in
manufacturing electrical items which involve complex patterns, such
as displays which include complex patterns of pixels. Other
applications include the fabrication of aerials or antenna for car
radios, mobile phones, and/or satellite navigation systems; radio
frequency shielding devices; edge connectors, contact and bus
connectors for circuit boards; radio frequency identification tags
(RFID tags); conductive tracks for printed circuit boards,
including flexible printed circuit boards; smart textiles, such as
those including electrical circuits; decorations; vehicle
windscreen heaters; components of batteries and/or fuel cells;
ceramic components; transformers and inductive power supplies,
particularly in miniaturised form; security devices; printed
circuit board components, such as capacitors and conductors;
membrane keyboards, particularly their electrical contacts;
disposable, low cost electronic items; electroluminescent
disposable displays; biosensors, mechanical sensors, chemical and
electrochemical sensors.
[0111] The method also finds application in producing an electrical
connection between two components in or for a circuit.
[0112] The method may also be used to produce decorative
features.
[0113] The method may include the further step of forming an
additional metal layer onto a conductive metal region constituted
by the second layer, e.g. by electrolytic or electroless plating or
by immersion metallisation.
[0114] Where the first liquid, and/or the second liquid, are inkjet
printed, the respective liquids should fulfil the specific
requirements of inkjet printing inks as regards viscosity, surface
tension, conductivity, pH, filtration, particle size and ageing
stability. One or more humectants may be added to one or more
component solutions to reduce evaporation. The particular values of
these properties which are required are different for different
inkjet technologies and suitable component solutions fulfilling
these properties can readily be devised for a specific application
by one skilled in the art.
[0115] The method also extends to an article prepared according to
the method of the invention.
[0116] According to a further aspect of the present invention there
is provided a liquid comprising a curable layer-forming composition
for forming a first solid layer on the surface of a substrate, the
liquid comprising an activator suitable for activating a second
layer-forming chemical reaction, and one or more chemical
components which are capable of undergoing a chemical reaction
(typically responsive to a stimulus) causing the liquid to
harden.
[0117] The invention also covers the activator liquid in
combination with a second fluid.
[0118] Preferably, the one or more chemical components comprise
monomers and/or oligomers which can polymerise, forming a solid
first layer.
[0119] The activator is preferably a catalyst. However, the
activator could comprise a chemical species which can activate the
second solid layer forming chemical reaction but which is consumed
or reacts in the process.
[0120] The activator may also comprise a reagent, or a plurality of
reagents which, when brought into contact with a second liquid
comprising components (preferably other components) of a second
layer-forming chemical reaction, undergo a chemical reaction
leading to formation of a second layer on the first solid
layer.
[0121] Suitable solvents for the deposition of an organic acid salt
of a transition metal include diacetone alcohol, mixtures of equal
amounts by weight of diacetone alcohol and methoxypropanol, and
mixtures of equal amounts by weight of toluene and methoxypropanol.
A co-solvent is preferably included to increase viscosity to
suitable levels for inkjet printing. Preferably the organic acid
salt of a transition metal constitutes 1-3% by weight of palladium
acetate, most preferably 2% by weight of the deposited liquid. An
equivalent concentration of another organic acid salt of a
transition metal can be employed.
[0122] Preferred features of the layer-forming activator solution
are as discussed above.
[0123] In a further aspect of the present invention there is
provided a method of forming on the surface of a substrate a first
layer which is suitable for activating a second solid layer-forming
chemical reaction thereon, the method comprising the steps of:
applying a curable liquid to the surface of the substrate, the
curable liquid comprising an activator for a layer-forming chemical
reaction; and curing the curable liquid, thereby forming a first
solid layer on the surface of the substrate, capable of activating
a second solid layer-forming chemical reaction.
[0124] The invention also extends to a method of forming a solid
layer on a substrate, comprising the steps of: applying a curable
liquid to the surface of the substrate, the curable liquid
comprising an activator for a layer-forming chemical reaction;
curing the curable liquid, thereby forming a first solid layer on
the surface of the substrate, capable of activating a second
solid-layer-forming chemical reaction thereon; and bringing into
contact with the first solid layer a second liquid comprising
components of a second solid-layer-forming chemical reaction,
activated by the activator, thereby causing a second solid layer to
be formed on the first solid layer.
[0125] The invention will be further described, by way of
illustration, in the following Examples. In the Examples all
percentages are percentages by weight unless otherwise
specified.
EXAMPLE 1
[0126] UV curable catalyst formulations referred to as ALF 116 and
ALF 117 were prepared according to the formulation shown in Table 1
below. The monomers, oligomers and initiators used are already
known from the related field of WV curable inkjet inks to have
excellent curing properties and adhesion to plastic substrates.
These formulations contain some solvent (diacetone alcohol and
methoxy propanol) acting as a carrier liquid in which the palladium
acetate catalyst is soluble. The solvent was allowed to evaporate
off after application of the formulation to a Melinex (Melinex is a
Trade Mark) polyester substrate surface by inkjet printing using an
XJ500/180 print head from Xaar, UK. The inks were then cured by the
application of UV which began a curing procedure in which the
monomer and oligomer components polymerised.
UV Curable Catalyst Formulations
Figures are Percentages by Weight
[0127]
1 TABLE 1 Materials ALF 116 ALF 117 Palladium acetate 1.25 0.94 PVP
K30 -- 2.5 Diacetone alcohol (DAA) 24.38 23.28 Methoxy propanol
24.37 23.28 Actilane 505 5 5 DPHA 1.5 1.5 Irgacure 1700 3.25 3.25
Irgacure 819 1.25 1.25 DPGDA 39 39
[0128] PVP K30 is a grade of polyvinyl pyrrolidinone supplied by
ISP, Tadworth, UK. Actilane 505 is a UV-curable reactive
tetrafunctional polyester acrylate oligomer supplied by Akzo Nobel
UV Resins, Manchester, UK. DPHA is dipentaerythritol hexacrylate, a
IV-curable hexafunctional monomer, supplied by UCB, Dragenbos,
Belgium. Igracure 819 and Igracure 1700 are UV photo-initiators
supplied by Ciba Speciality Chemicals, Macclesfield, UK--Irgacure
is a Trade Mark. DPGDA is dipropylene glycol diacrylate, a
UV-curable reactive diluent monomer supplied by UCB, Dragenbos,
Belgium. The monomers and oligomers are in liquid form. Diacetone
alcohol and methoxy propanol are solvents for the palladium
acetate.
[0129] PVP constitutes a water soluble (second) chemical
functionality. The monomers and oligomers, Actilane 505, DPHA and
DPGDA, react to form a polymer that constitutes a water insoluble
(first) chemical functionality.
[0130] ALF 116 cured well (with a line speed of 40 metres/minute)
to give a tough scratch resistant film. However, when a copper
layer forming solution (consisting of Enplate 872A (30% w/w),
Enplate 872B (30% w/w), Enplate 872C (10% w/w), t-butanol (5% w/w),
ethylene glycol (20% w/w) and polyethylene glycol 1500 (5% w/w) was
applied to the film, no copper was deposited. We believe that this
is due to the smooth, impervious surface of the cured film, which
seals the catalyst into a plastic layer and prevents it from coming
into contact with the copper-layer forming solution.
[0131] Enplate 872A, 872B and 872C are copper plating solutions,
available from Enthone-OMI of Woking, UK. Enplate 872A contains
copper sulphate. Enplate 872B contains a cyanide complexing agent
and formaldehyde. Enplate 872C contains sodium hydroxide. (Enplate
is a Trade Mark.) Enplate 872 A, B and C are in common use as
component solutions for electroless copper plating. Ethylene glycol
is present as a humectant and acts to lower surface tension.
T-butanol is a cosolvent which reduces surface tension and
increases wetting. Polyethylene glycol-1500 functions as a
humectant.
[0132] In contrast, ALF 117 includes a small amount (5% by weight
of dried film) of polyvinylpyrrolidone, which was added to the
formulation with the aim that it would dissolve out of the cured
layer or swell or maintain permeability upon the subsequent
addition of the aqueous copper-layer forming solution, and
therefore expose the catalytic sites.
[0133] As with ALF 116, this again cured very well at 40
metres/minute and this time deposited copper (at a calculated 100
nm/minute).
[0134] Drying the substrate at 60.degree. C. for 24 hours resulted
in a material having good scratch resistance properties, as good as
the scratch resistance of the best catalyst formulation we know for
direct bonding of a copper-layer to a plastic substrate.
[0135] This work indicated that in order to maintain the activity
of the catalyst it was necessary to have some form of water
solubility, swellability, or other means to enable the second
liquid to penetrate the first layer.
EXAMPLE 2
[0136] Three further formulations referred to as ALF 120, ALF 121,
and ALF 124 were prepared as summarised in Table 2 below. Each of
these is a variant of ALF 117 from Table 1.
UV-Curable Catalyst Formulations
[0137]
2 TABLE 2 ALF 120 ALF 121 ALF 124 Palladium acetate 2 2 2 DPGDA 76
48 48 DPHA 3 3 3 Actilane 505 10 10 10 Irgacure 1700 6.5 6.5 6.5
Irgacure 819 2.5 2.5 2.5 Diacetone alcohol -- 12.75 14 Methoxy
propanol -- 12.75 14 PVP K30 -- 2.5 --
[0138] The formulations ALF 120, ALP 121 and ALF 124 were applied
to a Melinex polyester substrate, as described above in Example
1.
[0139] These inks were cured using a Fusion UV 500 Watt lamp fitted
with an H bulb (fusion is a Trade Mark), in a single pass at 10
metres/minute. After curing the inks were treated with DMAB
(dimethylamineborane) solution followed by a copper-layer forming
solution consisting of Enplate 872A (30% w/w), Enplate 872B (30%
w/w), Enplate 872C (10% w/w), t-butanol (5% w/w), ethylene glycol
(20% w/w) and polyethylene glycol 1500 (5% w/w). No copper was
deposited on ALP 120 or ALF 124. However, a good uniform layer of
copper was deposited on ALF 121. This copper layer was found to
have good conductivity, and good adhesion to the underlying
substrate. Since no copper was deposited on ALF 120 or ALF 124 this
provides further evidence that the PVP material is responsible for
maintaining the activity of the catalyst, and that it is likely
that this occurs via the water solubility mechanism proposed
above.
EXAMPLE 3
[0140] ALF 121 was then modified further to give an ink with good
properties for deposition by inkjet printing. Two such inks,
referred to as ALF 125 and ALF 126b, are shown in Table 3
below.
Jettable UV Ink Formulations
[0141]
3 TABLE 3 ALF 125 ALF 126b Palladium acetate 2 2 Irgacure 1700 3.25
3.25 Irgacure 819 1.25 1.25 DPGDA 61 48 DPHA -- 3 Actilane 505 --
10 Diacetone alcohol 15 15 Methoxy propanol 15 15 PVP K30 2.5 2.5
viscosity, cPs (25.degree. C.) 9.59 11.2
[0142] ALF 125 and ALF 126b both showed good inkjet printing
properties using a XaarJet 128-200 print head (available from Xaar
of Cambridge, England) and both gave good quality copper deposition
on a Melinex polyester substrate following the procedure described
above in Examples 1 and 2. However, when making thicker copper
samples of greater than 200 nm thickness, ALF125 blistered much
more easily than ALF 126b.
[0143] This is thought to be because ALF 126b contains higher
functionality materials (Actilane 505 is tetrafunctional, DPHA is
hexafunctional) and so is more highly cross-linked and therefore
forms a stronger, more robust film with better adhesion to the
substrate.
[0144] Based on these results, it is also thought that it should be
possible to replace the PVP with a water-swellable monomer such as
HEMA (2-hydroxyethyl methacrylate), GMA (glyceryl methacrylate) or
n (n-vinyl pyrrolidinone). Alternatively, a high boiling point
water miscible solvent such as NMP (n-methylpyrrolidinone),
ethylene glycol, diethylene glycol or glycerol could be used to
keep the UV-cured layer open, and to allow penetration by the
copper solution. Alternatively, a micro-porous film structure could
be prepared by the use of micro-porous particles, such as silica
(inorganic) or PPVP (poly polyvinyl pyrrolidinone) particles
(organic).
EXAMPLE 4
[0145] ALF 126b was then modified further to give a WV-curable
catalyst ink with optimised performance, known as ALF 126f. This
was used to deposit a conductive copper layer on a Melinex (Melinex
is a Trade Mark) polyester substrate. The composition of ALF 126f
was as follows:
ALF 126f Jettable UV Ink Formulation
[0146]
4 TABLE 4 ALF 126f Palladium acetate 2 Irgacure 1700 3.25 Irgacure
819 1.25 DPGDA 30.5 DPHA 3 Actilane 505 10 Diacetone alcohol 47.5
PVP K30 2.5 Viscosity, cPs (25.degree. C.) 17.6
[0147] This fluid was printed with a XJ500/180 print head
(available from Xaar of Cambridge, England) at 180.times.250 dpi.
The samples were then cured under a Fusion 500 Watt H-bulb, in 4
passes of 20 metres/min each, resulting in formation of the first
layer. For a line printed using a single jet, the thickness was
measured at about 500 nm. For larger area coverage the layer
thickness will increase, possibly up to the theoretical maximum for
this printing resolution of 2.9 microns. The samples were submerged
in a chemical bath containing a solution of 1.6%
dimethylamineborane (DMAB) in deionised water, and processed at
40.+-.2.degree. C. for 2 minutes, followed by a deionised water
rinse, and drying. This treatment reduced the palladium acetate to
palladium metal, thus activating the catalyst. The samples were
then treated with a copper layer forming solution, the solution
consisting of 75% deionised water and ENPLATE Cu 872A, ENPLATE Cu
872B, and ENPLATE Cu 872C in the weight ratio 3:3:1, respectively.
The samples were immersed in the copper layer forming solution
under agitation for 2 minutes, while held at 45.+-.2C in a
temperature controlled bath.
[0148] As with ALF 126b, ALF 126f showed good inkjet printing
properties and gave good quality copper deposition.
EXAMPLE 5
[0149] ALF 126f ink was coated onto a Melinex 339 (Dupont Teijin
Films) polyester substrate using a 12 .mu.m drawdown bar. The
liquid film was then exposed to UV light through apertures
patterned in a 25 micron aluminium foil. The UV light source was a
Fusion systems F500 using an H bulb, giving a total UV dose of 0.70
J/cm.sup.2. The exposed areas of the film cured and solidified. The
unexposed areas remained liquid and were easily washed away using
ethanol. A further four passes under the UV lamp ensured fall
curing.
[0150] The films were then immersed in a 1.6% solution of DMAB at
40.degree. C. for 2 mins, washed and then placed in an electroless
copper plating bath (Enplate Cu 872A, Enplate Cu 872B and Enplate
Cu 872C in the weight ratio 3:3:1, respectively) at 45.degree. C.
for 2 minutes and then rinsed again in deionised water. Copper
metal was plated onto the exposed regions whereas the unexposed
areas remained uncoated.
EXAMPLE 6
Direct Laser Writing
[0151] Structures were directly written using the process of direct
laser writing. Liquid films of ALF 126f ink of between 12 microns
and 24 microns were prepared on a Melinex 339 polyester substrate
(Melinex is a trademark of Dupont Teijin Films) using the draw-down
method. The liquid films were immediately fed into an Orbotech
DP100 SL Direct laser write system (Orbotech is a Trade Mark). This
system uses a 4 W Paladin (Paladin is a Trade Mark) diode pumped
solid state laser (Coherent Ltd) operating at 355 nm.
[0152] Patterns were produced using energy dosed from 20 mJ up to
100 mJ in an atmosphere of nitrogen gas (although this is not
essential). The uncured areas were washed away using ethanol. The
samples were then immersed in a 1.6% solution of DMAB for 2
minutes, rinsed in DI water and then plated by immersion in Enplate
copper plating solution (Enplate Cu872A, Enplate Cu 872B and
Enplate 872C in the weight ratio 3:3:1, respectively) for 2 minutes
at 45.degree. C. This resulted in well adhered copper features as
fine as 20 microns.
* * * * *